1. Field of the Invention
The present invention relates to a planographic printing plate precursor, and particularly to a planographic printing plate precursor which can provide a uniformly coated printing plate surface with excellent adhering ability and without such production failures as foaming.
2. Description of the Related Art
The planographic printing plate precursor comprises an image forming layer formed from an image forming composition on a support substrate, prepared by an image forming means causing an imagewise material change resulting in the division into a recording layer, and a non-image portion which is a hydrophilic an image portion which is hydrophobic. The planographic printing plate is obtained by the typical printing process wherein the hydrophilic non-image portion receives dampener and the lipophilic image portion receives ink to form an ink image. The ink image is transferred directly or indirectly to a desired printing medium to thereby obtain a printed product.
A negative type recording means which changes material from a soluble state to an insoluble state and a positive type which recording means changes material from an insoluble state to a soluble state are known for the image forming composition to be used for this process. Photo-reaction by exposure, a heat mode process, and a thermal recording system by heating are various techniques known for recording. Whatever image forming mechanism is used, planographic printing plate precursors that provide high quality images must have a highly uniform image forming layer, excellent hydrophobic ability in the image portion, and a strong ability to remove the non-image portion by developing. The damaging of the uniformity of the image forming layer is primarily related to the production steps. Insufficient uniformity in the master plates remarkably deteriorates the stable production of large numbers of high quality and highly uniform printed products, which is a fundamental necessity in printing.
Also, in order to attain high quality images, it is necessary for the image portion to have sufficient recording layer strength and good ink adhering ability. It is important for the non-image portion to be superior in the removal of the image forming layer by developing, to be free from the presence of a residual film, and to enable the exposing out of a support surface excellent in its hydrophobicity. However, strengthening the image portion region and improving its developing durability causes developing failures in the non-image portion region. Therefore the question of developing a planographic printing plate precursor capable of forming a high quality images superior in discrimination during developing has become important.
For example, technologies in which a macromolecular compound having a fluoro-aliphatic group contained in an image forming composition for the purpose of improving the uniformity of the image forming layer are disclosed in Japanese Patent Application Laid-Open No. 54-135004. This macromolecular compound can be said to be superior in that it has a high surface activity, that it is useful for improving the uniformity of the image forming layer, and in that it is highly hydrophobic and has the effect of improving developing durability because of its ability to orient to the surface of the image forming layer. However, with the improvement in developing durability there has been an undesirable reduction in developing ability, on print-making and the printing process. Therefore, technologies that improve these drawbacks using a copolymer containing a monomer unit comprising a fluoro-aliphatic group and a monomer unit comprising a specific functional group have been investigated. For instance, an attempt to improve surface activity by the introduction of other functional groups is stated in Japanese Patent Application Laid-Open (JP-A) No. 62-170950. A solution to the problem or the delay in developing created by hydrophobic characteristics is disclosed in JP-A No. 8-15858. The effect obtained by the formation of a high contrast image by the compatibility of the hydrophobic characteristics of the image line portion and the removability of the non-image line portion by making use of the hydrophobic characteristics and orientating force is disclosed in JP-A No. 2000-19724.
A macromolecular compound with a monomer unit comprising two or more fluoro-aliphatic groups to obtain an image forming material superior in the discrimination of the solubility of the image line portion and the non-image line portion is disclosed in JP-A No. 2000-187318.
As stated above, utilizing the image forming layer containing a fluoro-aliphatic compound may improve the efficiency of the planographic printing plate precursor to a certain degree, but it is still insufficient and creates the desire for further improvement.
In a case using a positive type image forming layer, as disclosed in JP-A No. 7-285275, an image recording material comprises an aqueous alkali solution-soluble resin to which a material that absorbs light to generate heat and a positive type light-sensitive compound such as quinonediazide compounds are added. The positive type light-sensitive compound works as a dissolution inhibitor which substantially decreases the solubility of the aqueous alkali solution-soluble resin in the image portion, but is decomposed by heat in the non-image portion, so that the dissolution inhibitive ability does not manifest, and it can be removed by developing to, thereby form an image.
It is also known that onium salts and compounds capable of forming a hydrogen bond network reduced in alkali solubility have the ability to inhibit the dissolution of an alkali-soluble polymer in an alkali. A positive action composition using a cationic infrared absorbing dye as an inhibitor restricting the dissolution of the aqueous alkali-soluble polymer for image recording materials using an infrared laser is described in WO 97/39894. This positive action means an action resulting in the formation of an image by using an infrared absorbing dye to absorb laser light, and by utilizing the generated heat to make the polymer film of the irradiated portion lose its dissolution inhibitive effectiveness.
Examples of a method of forming a negative type image forming layer include a recording system which uses an acid generated by light or heat as a catalyst. Heating after exposure causes the condensed crosslinking reaction, thereby curing the recording layer of the exposed portion to form the image portion. JP-A No. 7-271029 describes known techniques for a printing plate having such an acid catalyst crosslinking type recording layer. Another example is a recording system in which a polymerization reaction is caused by using a radical generated by light or heat as an initiator to cure the recording layer of the exposed portion to form the image portion. Known techniques for using a photopolymerizable or thermally polymerizable composition as a light-sensitive layer for the printing plate having a recording layer polymerized by light or heat are described in JP-A Nos. 8-108621 and 9-34110.
Image formation of the aforementioned recording materials accords with a sufficient supply of laser reduced energy for an image forming reaction on the surface of the sensitive material. However, a case using a common aluminum support has the problem of the significant heat diffusion to the support because of its good heat conductivity, so that an insufficient amount of energy is utilized for the formation of the image, creating the problem of low sensitivity. Also, there is the problem of not obtaining sufficient elimination of the dissolution inhibition or the effect of promoting an effective reaction by polymerization in the deeper areas of the sensitive material. The result is that contamination of the non-image portion caused by residual film tends to occur for the positive type and insufficient image strength with inferior anti-scratching ability is obtained the negative type.
In order to obtain good printed products, planographic printing plate precursors having as high a discrimination as possible for the image and non-image portions are preferable in view of the reproduction of the image and anti-scratching ability. A precursor that makes highly sensitive recording possible and enables handling under white light is also sought.
An object of the present invention is to solve the aforementioned problems by providing a planographic printing plate precursor superior in the uniformity of its image forming layer, that enables highly sensitive recording, has good hydrophobic characteristics for the image portion of the surface, possesses excellent resistance to the developing solution, has adhering ability and printing durability, and is superior in the removal of a non-image portion.
The inventors of the invention have proceeded with earnest studies and as a result, found that the above object can be attained by adding a macromolecular compound (hereinafter referred to as a specified fluorine macromolecular compound when required) comprising a specified fluorine type structural unit in the image forming layer, and so have thereby completed the invention.
Accordingly, a planographic printing plate precursor according to the invention comprises an image forming layer containing a fluorine macromolecular compound having a structural unit derived from a monomer represented by the following general formula (I) on a support. 
wherein R0 represents a hydrogen atom, a methyl group, a cyano group or a halogen atom, X represents a single bond or a divalent connecting group, R1 to R6 each independently represent a hydrogen atom, an alkyl group, a fluorine atom or an alkyl group in which at least one hydrogen atom is substituted with a fluorine atom; wherein at least one of R1 to R6 represents a fluorine atom or an alkyl group in which at least one hydrogen atom is substituted with a fluorine atom.
Those monomers represented by the general formula (I) in which X is xe2x80x94CH2xe2x80x94 or xe2x80x94Phxe2x80x94 are preferable.
Also, those fluorine macromolecular compounds comprising at least one structural unit derived from poly(oxyalkylene)acrylate and/or poly(oxyalkylene)methacrylate, besides the aforementioned fluorine type structural unit and a structural unit derived from a monomer represented by the following general formula (II), are preferable embodiments. 
wherein R0 represents a hydrogen atom, a methyl group, a cyano group or a halogen atom, Y represents a single bond or a divalent connecting group, and R7 represents an alkyl group having 1 to 20 carbon atoms.
Although how the materials effect the carrying out of the invention is not precisely clear, it is considered that since the image forming layer contains the aforementioned specified fluorine macromolecular compound, this polymer provides during the step of forming an image forming layer on the support, a uniform coated surface without any surface abnormalities caused by the foaming of the coating solution due to its excellent surface activity. A uniform image forming layer is obtained thereby restricting local reductions in sensitivity caused by a lack in uniform thickness. Also the hydrophobic characteristics of the layer improve the ink adhering ability.
Moreover, the addition of a fluorine macromolecular compound ensures by the functioning of the fluorine type structural unit localized on the surface that image strength in the vicinity of the surface is improved along developing durability. Excellent discrimination and the limitation of fogging caused by diffused and reflected light in the laser light-sensitive photopolymerizable image forming layer means that a higher printing durability can be expected.
In a positive type image forming layer, the carrying out of the same operative action also enlarges discrimination and heightens image strength so that the image, even a portion touched with a bare hand, does not fall away, showing improvement in stability against harmful external effects.